The invention relates to a clutch-actuating device, in particular for use in the power train of a motor vehicle. The invention further relates to a method of determining a closed clutch position, a method of determining the actuating force of a clutch, as well as a method of determining the temperature of an actuator motor.
Automated clutches are being used to a growing extent not only for the increase in comfort that they provide but also for their potential advantage to save fuel in motor vehicles.
The block diagram of FIG. 9 shows an example of a power train of a motor vehicle that is equipped with an automated clutch. The power train includes a combustion engine 2, a clutch 4 and a transmission 6. A drive shaft 8 leads from the transmission to the driven wheels, which are not shown in the drawing. The transmission 6 consists, e.g., of an automated manual-shift transmission or a cone-pulley transmission with a steplessly variable transmission ratio. The transmission 6 is actuated or shifted by means of an actuating device 9 which is controlled in a conventionally known manner from a selecting device 10 by means of a selector lever 12 and through a control device 14. As is self-evident, the selecting device can also be configured differently, for example as a conventional stick-shift lever (H-pattern) or as a lever with tipping positions for up-shifting and down-shifting. The clutch 4 is configured, e.g., as a friction disc clutch of a conventional design with an actuating device 16 based on a hydraulic, electrical, electro-hydraulic, or other working principle.
The inputs of the control device 14 are connected to sensors which may be arranged in the power train. The sensors may include, e.g., a pressure sensor 18 to determine the intake suction pressure of the engine 2, an rpm-sensor 20 to determine the rpm-rate nM of the engine crankshaft, a sensor 22 to detect the depression angle α of an accelerator pedal 24, a sensor 26 to detect the position of the selector lever 12, and a further rpm-sensor 28 to determine the rpm-rate of the drive shaft 8.
The control device 14 contains a conventional arrangement of a microprocessor with associated storage memory 29 where characteristic data arrays and programs are stored that are used to control actuators such as an engine-load actuator 30 of the engine 2, the actuating device 16 of the clutch 4, as well as the actuating device 9 of the transmission 6. The individual actuators can be based on a functional principle in which the actuator position is directly known in the control device 14 as is the case, e.g., with stepper motors, or the actuator position can be determined by an additional position sensor such as the position sensor 32 for determining a parameter that is indicative of the position SK of the clutch.
The design and function of the foregoing system are known per se and are therefore not discussed in detail. Depending on the driver's input that is communicated through the accelerator pedal 24 or the driver's request for a program mode or forward/reverse direction as communicated through the selector lever 12, the engine-load actuator 30, the clutch-actuating device 16, and the transmission actuator 9 are operated in a mutually coordinated process dependent on the sensor signals, resulting in a comfortable and/or economical driving behavior of the vehicle.
For example, a memory location of the control device 14 contains a characteristic data set for the actuation of the clutch 4, correlating a target position of the clutch-actuating device 16 to a specific amount of torque to be transmitted by the clutch 4. For reasons related to the control loop quality, the wear on the clutch and the energy consumption of the actuating device, the transmittable clutch torque at a given time should be set no higher than absolutely necessary. The amount of torque that needs to be transmitted through the clutch is based on the driver's input, i.e., the position of the accelerator pedal 24, and the engine load of the combustion engine 2 as detected, e.g., by the sensor 18. Additional operating parameters such as, e.g., the engine rpm-rate, may also enter into the determination of the transmittable torque.
The characteristic data set stored in the control device 14 for the functional correlation between the displacement target of a clutch-actuating member operated by the actuator device 16 and the calculated amount of torque to be transmitted by the clutch has a critical influence on a comfortable start-up behavior of the vehicle as well as a comfortable gear-shift experience. The correlation is subject to short-term fluctuations, for example due to temperature changes, as well as long-term drift over the lifetime of the clutch, for example as a result of wear. The characteristic correlation between actuator displacement and clutch torque under specific operating conditions is therefore continuously monitored according to a diversity of strategies, and the affected control parameters are adapted.
An example of an actuating device 16 is shown in detail in FIG. 10.
A piston 38 moving in a hydraulic master cylinder 36 has a shaft 40 with a spindle profile that engages an internal thread of a gear 41 which, in turn, meshes with a pinion gear 42 of an electric motor 43 that is controlled by the control device 14 (FIG. 4). The electric motor can be of any appropriate type and is controlled, e.g., by a pulse-width-modulated signal. A stepper motor represents an advantageous choice. The master cylinder 36 has a snifting bore 44 connected to a compensation reservoir (not shown) by way of a conduit 45. A conduit 48 leads from the pressure compartment 46 of the master cylinder 36 to a slave cylinder 50 containing a piston 52 connected for example by a piston rod to the clutch release lever 54 which represents an actuating element. The position A, generally referred to as the snifting position, represents the point at which the build-up of clutch-actuating pressure begins in the pressure compartment 46 after the piston 38 has moved to the right of point A in FIG. 11.
In the illustrated example, an incremental position sensor 32 of a conventional type is arranged at the gear 41, counting the number of gear teeth moving past the sensor by sending pulse signals to the control device 14. The number of pulses is a direct measure of the displacement of the master-cylinder piston 38. When the piston 38 is in a position to the right of the snifting position A in FIG. 9, the number of pulses also represents a measure for the displacement of the clutch release lever 54.
In a so-called snifting phase, the master-cylinder piston 38 is moved to the left beyond the snifting position A, so that the hydraulic connection between the pistons 38 and 52 is connected to the conduit 45 and thus relieved of pressure. It is advantageous if the master-cylinder piston 38 has a check valve (not shown) that opens if there is an overpressure to the left of the piston 38. In the pressure-free state of the hydraulic line, the release lever 54 takes a position that represents the fully engaged state of the clutch. As the master-cylinder piston 38 is subsequently moved to the right by the electric motor 42, the release lever 54 is actuated from the moment at which the master-cylinder piston 38 moves past the snifting position A. This position of the piston 38 can be detected in a diversity of ways. The corresponding pulse count of the incremental position sensor 32 is stored in the control device 14 as a reference parameter, hereinafter referred to as the closed position of the clutch.
Seen as an overall system, the actuating device according FIG. 10 represents a transfer mechanism in which a small, substantially constant force K moves the master-cylinder piston 38 inside a range 1 (FIG. 11) to the left of the snifting position A, and an increasing amount of force K is required to move the master-cylinder piston to the right after passing over the snifting bore, i.e., in range 2 (FIG. 11) to the right of the position A, to disengage the clutch against the opposing force of the clutch pressure spring. A linear force/displacement characteristic of the clutch was assumed in the example of FIG. 11.
The foregoing arrangement of the clutch-actuating device with two different ranges, where the transition point corresponds to a defined clutch position, preferably the fully engaged position of the clutch, has the significant advantage that the defined clutch position can be reliably detected in the manner described above.